Before checking the idle mixture on any engine, what should be done first?

Warming the engine to normal temperatures is a critical step before checking the idle mixture because the engine's operating characteristics, including fuel vaporization and combustion efficiency, change significantly at different temperatures. When the engine is cold, fuel may not atomize correctly, leading to inaccurate readings and potentially skewed adjustments.

Once the engine reaches its normal operating temperature, it ensures that the fuel mixture is representative of typical driving conditions, thereby providing a more accurate basis for tuning the idle mixture. This step is essential in achieving optimal engine performance, fuel efficiency, and emissions control. Adjusting any other settings or performing checks without the engine being at the correct temperature could lead to misdiagnosis or improper adjustments, thus possibly harming engine performance.